The drill spindle of a drilling machine for glass is usually journaled for rotation in a carrier, or similar receiving member, and it is equipped with a main drill at the end directed towards the workpiece, as well as being equipped with a chamfering drill, countersink, counterbore, or like second drill means, which generally surrounds the first or primary drill. The drill and the chamfering drill must be axially adjustable with respect to one another, in accordance with the wear of the main drill, which is accelerated with respect to the countersink so as to compensate for such wear.
The drill is then connected in a drill carrier or receiver by way of adjustment threads. The drill is preferably a core drill. Advancing of the drill spindle is done with or relative to the drill spindle carrier.
It wil be understood, moreover, that drilling machines for drilling glass are usually operated with drill spindle pairs, wherein each individual assembly is identical to the other in the pair up to the coolant feeding means.
The main drill and the chamfering drill of each unit are fed toward the coring drill and countersink of the other unit from above and below the glass pane and meet to form the bore.
The prior art drill apparatus for this purpose have manual means for effecting adjustment of the relative positions of the main drill and the countersink or chamfering drill. This is labor intensive and must be done with great care by highly specialized personnel. Moreover, the adjustment must be made in very small increments of the order of a millimeter.